Heater for asphalt concrete roadways and the like

ABSTRACT

Fuel such as pentane is heated to 300* F to 400* F and then mixed with the air needed to oxidize the carbon and produce a smokeless exhaust. The mixture is delivered into a shallow chamber of which the pavement to be heated is the bottom. The roof of the chamber is of infra-red brick and has depending side walls and end walls extending down close to the pavement to be heated, providing heat-radiating surfaces. The spent gases are aspirated through holes in the roof near its edges to keep the pressure in the chamber automatically identical with the atmospheric pressure outside. The intensity and rapidity of the heat transfer into the roadbed is such that exposure to the naked flame in the chamber can only be continued for a fraction of a minute without getting the surface hot enough to injure the pavement. The completion of the process is as disclosed in my earlier U.S. Pat. No. 3,361,042 and includes roweling all the softened roadbed to dislodge heated material and additional cooler material lower down, and a second heating of the roweled surface.

United States Patent 091 Cutler 1 1 Apr. 3, 1973 [54] HEATER FOR ASPHALTCONCRETE [57] ABSTRACT ROADWAYS AND THE LIKE Fuel such as pentane isheated to300 F to 400 F and [75] Inventor: Earl F. Cutler, Lawrence,Kans. then mixed with the air needed to oxidize the carbon and roduce asmokeless exhaust. The mixture is [73] Asslgnee' Eggs Repaying Lawrencedeliv red into a shallow chamber of which the pavement to be heated isthe bottom. The roof of the [22] Filed: Mar. 30, 1971 chamber is ofinfra-red brick and has depending side walls and end walls extendingdown close to the pave- [21] Appl' 129404 ment to be heated, providingheat-radiating surfaces. The spent gases are aspirated through holes inthe roof [52] U.S. Cl. ..l26/27l.2 A near' its edges to keep thepressure in the chamber au- [51] Int. Cl ..E0lc 23/14 tomaticallyidentical with the atmospheric pressure [58] Field of Search...l26/27l.2R, 271.2 A, 271.2 C outside. The intensity and rapidity of the heattransfer into the roadbed is such that exposure to the naked [56]References Cited flame in the chamber can only be continued for afraction of a minute without getting the surface hot UNITED STATESPATENTS enough to injure the pavement. The completion of the 1,458,0706/1923 Long m1 .Q ..126/27l.2AX P as disclosed in y earlier 3,279,45810/1966 Moench ..126/271.2 A 3,361,042 and includes roweling all thesoftened 2,566,473 9/1951 Wilson ..126/271.2C roadbed to dislodge heatedmaterial and additional 3,311,104 3/1967 Wollner et a1. ..l26/27l.2 A Xcooler material lower down, and a second heating of 1,500,340 7/1924Smith "126/2712 A th led urfa 1,736,227 11/1929 .....126/271.2 A1,961,877 6/1934 Gars ..l26/27l.2 A 11 Claims, 9 Drawing Figures PrimaryExaminer-Charles J. Myhre Attorney-Olson, Trexler, Wolters & BushnellPATENTEUAFM I975 3 724 445 SHEET 1 [IF 3 M m, was UM;

HEATER FOR ASPHALT CONCRETE ROADWAYS AND THE LIKE SUMMARY OF THEINVENTION A readily combustible hydrocarbon such as pentane isintimately mixed in gaseous condition with all the air needed to oxidizeall the carbon to carbon dioxide, and produce a smokeless exhaust freeof pollutants. The pentane is usually received in liquid form and ischanged to gas in a combined pilot light and vaporizer at one corner ofthe chamber. A small ordinary blowtorch constituting a' pilot burnerdelivers a small jet of flame to one or two adjacent main heatingburners, and .a coil of metal tubing wound around the pilot burnerreceives liquid pentane, and delivers it at about 350 F in gaseous form.Combustion is accelerated by preheating the fuel to temperaturesbelieved to result in a small amount of cracked nascent material. 300 Fto 400 F is found to get good results in getting rapid blue flameburning later.

Air is compressed in a conventional blower to a suitable pressure suchas nineteen inches of water column. The freshly heated fuel is mixedthoroughly with the air and the mixture is delivered to burners that arein a shallow chamber of which the pavement to be heated is the bottom.The burners are disposed in such pattern that the chamber has amultiplicity of closely spaced flames that substantially fill thechamber with lambent flame. The rest of the chamber is an insulatingroof with narrow depending side walls along its periphery extending downclose to the pavement to be heated. The 'spent effluent is exhaustedthrough the roof at its periphery to keep the pressure in the chamberautomatically substantially the same as the atmospheric pressureoutside.

The solid roof and sidewalls are adapted to radiate most of their heatin red and infra-red wavelengths. The entire chamber fills with gentlebluish flame transparent to the long wave length heat from the radiantroof and side walls. Radiant screens associated with some of the burnersradiate energy in the ultra red visible spectrum for effectivelydelivering heat energy to pebbles and other non-black material in theroadbed.

The intensity and rapidity of the heat transfer into the roadbed is suchthat exposure to the naked flame in the chamber can only be continuedfor a fraction of a minute without getting the surface hot enough toinjure the pavement. The operator controls the time duration of heatingby varying the speed of the roof over th pavement.

The completion of the process is as disclosed in my earlier U.S. Pat.No. 3,361,042 and includes roweling all the softened roadbed to dislodgeheated material and additional cooler material lower down, and a seconddelivery of heat to the roweled surface followed by conventionalsmoothing and cooling.

BRIEF DESCRIPTION OF THE FIGURES In the accompanying drawings:

FIG. 1 is a view partially structural and partially a functional diagramof one heating unit and taken approximately along line I- l of FIG. 2,

FIG. 2 is a plan view looking downward approximately along line 2-2 ofFIG. 1 showing one corner of the chamber;

FIG. 3 is a vertical fragmentary section taken approximately along line3--3 of FIG. 2;

FIG. 4 is a similar fragmentary section taken approximately along line4--4 of FIG. 2;

FIG. 5 is a fragmentary sectional view taken on a vertical plane throughone of the lower burners;

FIG. 6 is a fragmentary sectional view of the fuel-air mixing chambertaken along line 6-6 of FIG. 1;

FIG. 7 is a fragmentary sectional view taken along line 77 of FIG. 2;

FIG. 8 is a fragmentary sectional view taken on a vertical plane throughone of the upper burners as seen from line 8-8 of FIG. 1; and

FIG. 9 is an enlarged fragmentary sectional view taken along line 9--9of FIG. 8. 1

DETAILED DESCRIPTION In the embodiment of equipment selected forillustration, the machine is of the general type disclosed in myaforesaid U.S. Pat. No. 3,361,042 and the present invention is animproved heating unit for such machines. The heating unit comprises amain roof 10 that is 10 or 12 feet long in the transverse dimensionindicated in FIG. 1, and about 6 feet wide in the direction of movementalong over the pavement 12. A continuous peripheral side wall 15completely encloses the edges of the chamber 14 between the roof l0 andthe pavement 12. The wall 15 extends so that there is a small crack 17between the wall 15 and the pavement 12. The side wall 15 includes endportions 16 at the lateral ends of the roof 12 which have smalllongitudinal grooves 18 adapted to receive the reversely hooked edges 20of laterally extending baffles 22 to obstruct drafts striking theequipment from the side from getting under the edges of the side wallsin sufficient volume to disturb the heating taking place inside.

These baffles 22 may be in short sections and each section may overlapan adjacent section. The baffles may be needed in windy weather.

As seen in FIG. 1, a conventional rotary fan 26 with an axial inlet at28 compresses air to a working pressure equivalent to a water column ofnineteen inches, plus or minus 3 or 4 inches. The downwardly moving airpasses through conduit 27 into fuel-air mixer 29 having a mixing chamber32. The air in the chamber 32 is deflected into a vortex by curbed.guiding baffles 30 (See FIGS. 1 and 6). Fuel from pipe 33 enters thechamber 32 at two inlets 34, 34. The inlets 34 are located at differentradial distances from the center of Provided at one corner of thechamber 14 is a pilot burner 43 which is shown enlarged in FIG. 7 andwhich may take the form of a blow torch of conventional construction. Afuel line 45 is connected to a source of hydrocarbon fuel (such asliquid pentane) carried by the machine, the line 45 including a fuelsupply valve 47 which is open when the machine is in operation. The partof the fuel line 45 within the chamber 14 is formed in a coil 49 aroundthe burner tube of the pilot burner 43 so that incoming fuel may bepreheated. to about 350 F prior to being sent through supply pipe 33 ingaseous form to the mixing chamber 32. By preheating the fuel, asaforesaid, it has been found that a more efficient heating is providedby the burners 39, 41, resulting in more BTU s being delivered to thepavement 12.

Referring again to FIG. 7 the pilot burner 43 and coil 49 may be mountedin any convenient manner as by U- shaped sheet metal member 51 which issuspended from the roof l and with the intake end of the pilot burner 43projecting through the side wall 15. A suitable small pilot-lightingaccess (not shown) may be provided, and in addition there is a pilotsupply line 53 with a valve V.

Referring now to the top burner shown in FIGS. 8

and 9, the nylon tube 36 delivers the fuel-air mixture to a rigid metalstandard tube 38, which is embedded in the roof and extends down alongthe axis of a conical cavity in the lower face of the roof. The roofcavity is divided into a small, upper mixing chamber 40 by a spreaderplate 42, upon which rests a finely perforated diaphragm 44 with asupporting nut 46 below both. The gas from the tube 38 issues radiallythrough lateral out lets 48 and the slight turbulence in the smallchamber 40 completes the intimate mixing of the ingredients. Directlybelow these parts is the much larger annular cavity 50 in whichcombustion occurs, and the resultant flame spreads down gently from thediaphragm 44 within a contour indicated in dotted lines at 52. The lowerend of the tube 38 receives a bottom closure nut 54 with a threadedshank 56. A radiant screen 60 with large openings 61, rests in the upperportion of the flame, which spreads downwardly with gentle movement. Theexpansion of the flaming gas takes place in the lower annular cavity 50and the mouth of that cavity has a diameter about 12' times that of theinner diameter of the tube 38. The supporting nuts for the radiantscreen define a relatively stagnant space along the axis of the burnerand there will be a small relatively stagnant cone at the bottom of thenut 54. Contact with this obstacle will remove fractions of the coneunder the nut 54. The flame passing on down will move in to replacewhatever is removed. Along the axis of the tube 38 and below the nut 54,the central portion of the expanding flame will move downwardly a littlefaster than the outer lateral portions and the resulting relativelylarge quiescent bulb will extend down and gently spread out on thepavement below. The screen 60 is preferably of an alloy metal thatradiates in the visible spectrum of red and above. Such alloy may forexample be one containing about 3035 percent nickel, 19-23 percentchromium and the remainder iron.

Referring now to FIG. 5, the upstanding delivery tube 62 of burner 41receives combustible mixture from the nylon tube 37. The burner 41 isshaped to define an upper torus-like chamber 66 and the flame begins atthe end of the tube 62 and generates a vortex 68 in which rapidcombustion takes place. The flame issues through a central opening 70 inthe bottom of the upper chamber into a second substantially duplicatechamber 72 in which the central flow again engenders a complete closedtorus 74. By the time the gas reaches the bottom of the torus 74, it isalmost completely through burningand incandescent with a light bluetransparent flame. This central stream then starts down down and brushthe surface of the pavement gently and spread out into an outer torus76, almost three times the diameter of the torus 74. With eachenlargement of its cross section the stream decreases its linearvelocity in an inverse ratio and the merged mass of flame from all theburners. Thus, the combined action of the flames from the burners'39, 41results in a mass oflam bent flame that substantially fills the chamber14.

Referring to FIGS. 1 and 2, it is seen that adjacent to the corners ofthe roof 10 are groups of openings 80, 82, one group of openings beingat the long side of the roof l0 and the other group of openings 82 beingat the shortsideof the roof. One group of each of these openings 80, 82is shown in FIG. 2, it being understood that a like arrangement ispresent at the other three corners of the roof. Extending into theopenings 80, 82 are short pipes 83, 84 the upper ends of which arejoined by support plates 85, 86. The openings with the pipes thereinprovide an exit flow path' adjacent to the periphery of the chamber 14for the discharge of burnt gases.

Above the open upper ends of the pipes 83, 84am headers 88, 90, therebeing a pair of such headers 88, at each of the four corners of the roof10. The

headers receive the burnt gases and convey them to exhaust uptakes 92 ateach corner of the roof.'The gases then flow upwardly and to atmospherevia corner stacks 94.

Connected to the conduit 27 above the mixer 29 are aspirator tubes 96,there being one tube 96 extending to the bottom of each corner stack 94and opening therein. These aspirator tubes 96 result in a portion of theair stream from the fan 26 being utilized for providing a draft in thestacks 94, the remaining portion of the stream being sent to the mixer29, a previously described. By reason of the use of the aspirator tubes96 to produce the induced draft, the exhaust gases are withdrawn fromthe chamber 14 in an amount that is equal in volume but not in weight tothat of the fuel-air supply flow into the burners. Also, the aspiratingtubes 96 provide such effective draft that the stacks need only be highenough to permit the stream from the aspirating tube to blend with therest of the gases present, and the stacks can be short enough not to getin the way with branches of trees or the like along the side of theroad.

In staring an operation with liquid pentane, the pilot burner 43 isfirst lit and allowed to burn a minute or two to. warm up the tube 49.The pentane supply will issue immediately when the valve 47 is opened.There is also available gaseous pentane, which can pass through the sameequipment and get the same result. A

slightly lower working temperature in the intake end of the pilot burneritself is wiped outduring the subsequent heating of the gas. Theoperator will let the equipment remain stationary for from one to threeminutes depending on the temperature of the pavement, and then traversethe heater along the road as fully explained in my aforesaid earlierpatent. It will be obvious that when the weather is such that theambient temperature is say 40 F, the heating of the pavement to thedesired final temperature may take two or three times as long as wouldbe required on a day with the thermometer at 90 F in the shade. it willalso be obvious that the second heating (after the material warmed bythe first heating has been disturbed and mixed with cooler portionsdislodged from the underlying roadbed) causes the effective surfaceexposed to the action of the heater to be much greater. The temperaturegradient after the second heating will thus extend much farther down andstill be as hot at the top surface as is safe for the material of thepavement. The brick roof will deliver a maximum fraction of its radiantheat at red and infra-red wavelengths, which are the wavelengths mostreadily absorbed by the typical black asphalt concrete. However thescreens 60 for the top burners 39 are of a metal alloy that emits agreat deal of light of shorter wavelengths in the visible spectrum.These short wavelengths are separated from the pavement only by flamethat is substantially transparent to the short wavelengths so thatpebbles and other bits of material that are not black, and thus tend toreflect a great deal of any infra-red radiation, will receive theshorter wavelengths that are more effective in delivering radiant energyto such materials.

In the steady state operation, the mass of flame in the chamber 14 tendsto drift quiescently toward the discharge openings to the headers.Furthermore, by providing the discharge from the gases at the corners ofthe chamber 14, there is relatively little gas flow across the crack 17.

Others may readily adapt the invention for use under various conditionsof service by employing one or more of the novel features disclosed orequivalents thereof. For instance, it may sometimes happen that suitablepentane is not available and some other hydrocarbon in the general classof naptha or petroleum ether has to be used. If such a makeshiftsubstitute tends to smoke a littie, the air entering the inlet 28 can beseeded with the products of combustion rising in the stacks 94. For thispurpose there are indicated in FIG. 1, seeding tubes 98 with theirintake ends in the stacks 94 and their delivery ends at 100 in theintake opening 28. This can be designed and positioned to deliver from 5to 15 percent of the total volume drawn in by the main fan, and when thecompleted mixture gets into the flame it will already contain a littleionized material that will expedite the initiation and propagation ofthe flame and enhance the completeness of the combustion.

In addition to the advantages provided by the radiant heating and thepreheating of the fuel, the efficiency of the equipment is furtherenhanced by the arrangement and operation of the burners 39, 41. Thus,the burners cooperate to heat the walls of the chamber 14 only up to aneffective emission temperature sufficient to emit a maximum fraction ofradiation in the long red and infra-red wavelengths. The radiant screen60 in the upper burner 39 is in the flame at the level of maximum flametemperature and the spherical bulb of flame at 52 is approximately intangential contact with the pavement and the conical cavity of theburner. Burner efficiency is also enhanced by the fact that in the lowerburners 41 the gas is guided and retarded to issue into the chamber 14with a flow cross-section that is of many times greater than whereignition takes place, thus lowering the flame velocity in the chamber14. Furthermore, in the lower burner 41, the small upper and lowerchambers 66, 72 thereof form the gas into the small vortexes 68, 74 withtheir vertical axes in continuation of the direction of gas entry. Eachvortexis such that movement of the gas in circles in radial planescontaining the axis of the vortex reduces the linear distance flamepropagation must travel to reach every point in the circling mass. Also,the small vortex 74 changes into direct flow at the bottom of the burner41 to contact the pavement with a gentle flame.

The invention is claimed as follows:

1 Equipment for heating the upper strata of asphalt concrete pavement,or the like, comprising chamberforming walls including a roof walladapted to overlie an area to be heated by combined radiation and directcontact heating, and said walls including downwardly extendingperipheral side wall portions that leave only a small crack betweentheir lower edges and said pavement; power air blower supply and heatingmeans for producing a multiplicity of flames in said chamber below saidroof; said heating means comprising a multiplicity of burners thatproduce flames with cross-sections many times greater than whereignition takes place, said burners being disposed in a pattern such thatthe flames merge and form a substantially continuous mass of flameextending across said chamber to provide a substantially uniformtemperature to which the pavement exposed to said chamber is subjected;and exhaust means having an exit flow path through said chamber-formingwalls for removal of the products of combustion from within saidchamber.

2. Equipment according to Claim 1 in which said exhaust means is adaptedto withdraw from said chamber gases equal in weight but many timesgreater in volume than the mixture supplied to said chamber, whereby thestatic pressure inside said chamber at said crack is kept substantiallyequal to the atmospheric pressure outside.

3. Equipment according to claim 1, each burner having walls within whichthe expansion of the gases is guided and retarded.

4. Equipment according to claim 1 in which the burners are arranged in acheckerboard pattern in said chamber, the radially expanding lowerportion of each flame being arrested by encountering lower portions ofsurrounding flames.

5. Equipment for heating the upper strata of asphalt concrete pavement,or the like, comprising chamberforming walls including a roof walladapted to overlie an area to be heated by combined radiation and directcontact heating, and said walls including downwardly extendingperipheral side wall portions that leave only a small crack betweentheir lower edges and said pavement; power air blower supply and heatingmeans for producing a multiplicity of flames in said chamber below saidroof; said flames being spaced closely enough to merge and substantiallyentirely fill said chamber with quiescent lambent flame; exhaust meanshaving an exit flow path through said chamber-forming walls for removalof the products of combustion from within said chamber, each flame beingassociated with a burner, each burner having walls within which theexpansion of gases is guided and retarded to issue into the chamber witha flow cross-section many times greater than where ignition takes place,with corresponding reduction in linear velocity, certain of saidburners, identified for convenience as lower burners, defining smallchambers shaped to direct and entering stream of gas into small vortexeswith their vertical axes in continuation of the direction of entry,whereby the movement of gas in circles in radial planes containing theaxis of a small vortex substantially reduces the linear distance flamepropagation must travel to reach every point in the circling mass; theentire vortex changing into direct downward flow to contact thepavement.

6. Equipment for heating the upper strata of asphalt concrete pavement,or the like, comprising chamberforming walls including a roof walladapted to overlie an area to be heated by combined radiation and directcontact heating, and said walls including downwardly extendingperipheral side wall portions that leave only a small crack betweentheir lower edges and said pavement; power air blower supply and heatingmeans for producing a multiplicity of flames in said chamber below saidroof; said flames being spaced closely enough to merge and substantiallyentirely fill said chamber with quiescent lambent flames; and exhaustmeans having an exit flow path through said chamberforming walls forremoval of the product of combustion from within said chamber, certainof said flames originating in conical, downwardly opening cavities inthe lower surface of said roof, with ignition over a small circleintermediate the ends of said cones propagating radially both inward andoutward to build an approximately spherical bulb having tangentialcontact with its cone and with the pavement.

7. Equipment according to claim 6 in which an openmesh screen lies ineach flame, said screen being of material adapted to emit radiation ofrelatively short wavelengths efficient in heating light coloredmaterial.

8. Equipment for heating the upper strata of asphalt concrete pavement,or the like, comprising chamberforming walls including a roof walladapted to overlie an area to be heated by combined radiation and directcontact heating, and said walls including downwardly extendingperipheral side wall portions that leave only a small crack betweentheir lower edges and said pavement; power air blower supply and heatingmeans for producing a multiplicity of flames in said chamber below saidroof; exhaust means having an exit flow path through saidchamber-forming walls for removal of the products of combustion fromwithin said chamber, a

mixing chamber to receive compressed air from said power blower; fuelsupply conduit means for delivering fuel to said mixing chamber; and amultiplicity of mixture conduits, one for each flame, receivingcombustible mixture from said mixing chamber and delivering to eachflame its aliquot portion of mixture.

9. Equipment according to claim 8 in which said fuel supply conduitmeans has a portion having heat transfer contact with said blowtorch forpreheating the fuel en route to said mixing chamber.

10. Equipment for heating the upper strata of asphalt concrete pavement,or the like, comprising chamberforming walls including a roof walladapted to overlie an area to be heated by combined radiation and directcontact heating, and said walls including downwardly extendingperipheral side wall portions that leave only a small crack betweentheir lower edges and said pavement; power air blower supply and heatingmeans for producing a v multiplicity of flames in said chamber belowsaid ro'of; exhaust means having an exit flow path through saidchamber-forming walls for removal of the products of combustion fromwithin said chamber, and

conduit seeding means provided for returning to the inlet of said powerblower a minor fraction of the fresh exhaust gases from said chamber.

1 1. Equipment for heating the upper strata of asphalt concrete pavementor the like comprising chamberforming means including a roof foroverlying an area to receive the heat and downwardly extending wallportions that leave only a small crack between said wall portions andsaid area, means for producing a multiplicity of closely spaced flamessubstantially in said chamber such that the flames substantiallyentirely fill the chamber with lambent flame, and means defining an exitflow'path through said chamber-forming means for the removal of theproducts of combustion within the chamber; the wall surface of saidchamber being of a material that radiates a major-portion of its radiantheat at red and infra-red wavelengths, and said chamber also containinga multiplicity of members associated with respective flame producingmeans for radiating a substantial amount of energy in the visiblespectrum above red.

2. Equipment according to Claim 1 in which said exhaust means is adaptedto withdraw from said chamber gases equal in weight but many timesgreater in volume than the mixture supplied to said chamber, whereby thestatic pressure inside said chamber at said crack is kept substantiallyequal to the atmospheric pressure outside.
 3. Equipment according toclaim 1, each burner having walls within which the expansion of thegases is guided and retarded.
 4. Equipment according to claim 1 in whichthe burners are arranged in a checkerboard pattern in said chamber, theradially expanding lower portion of each flame being arrested byencountering lower portions of surrounding flames.
 5. Equipment forheating the upper strata of asphalt concrete pavement, or the like,comprising chamber-forming walls including a roof wall adapted tooverlie an area to be heated by combined radiation and direct contactheating, and said walls including downwardly extending peripheral sidewall portions that leave only a small crack between their lower edgesand said pavement; power air blower supply and heating means forproducing a multiplicity of flames in said chamber below said roof; saidflames being spaced closely enough to merge and substantially entirelyfill said chamber with quiescent lambent flame; exhaust means having anexit flow path through said chamber-forming walls for removal of theproducts of combustion from within said chamber, each flame beingassociated with a burner, each burner having walls within which theexpansion of gases is guided and retarded to issue into the chamber witha flow cross-section many times greater than where ignition takes place,with corresponding reduction in linear velocity, certain of saidburners, identified for convenience as lower burners, defining smallchambers shaped to direct and entering stream of gas into small vortexeswith their vertical axes in continuation of the direction of entry,whereby the movement of gas in circles in radial planes containing theaxis of a small vortex substantially reduces the linear distance flamepropagation must travel to reach every point in the circling mass; theentire vortex changing into direct downward flow to contact thepavement.
 6. Equipment for heating the upper strata of asphalt concretepavement, or the like, comprising chamber-forming walls including a roofwall adapted to overlie an area to be heated by combined radiation anddirect contact heating, and said walls including downwardly extendingperipheral side wall portions that leave only a small crack betweentheir lower edges and said pavement; power air blower supply and heatingmeans for producing a multiplicity of flames in said chamber below saidroof; said flames being spaced closely enough to merge and substantiallyentirely fill said chamber with quiescent lambent flames; and exhaustmeans having an exit flow path through said chamber-forming walls forremoval of the product of combustion from within said chamber, certainof said flames originating in conical, downwardly opening cavities inthe lower surface of said roof, with ignition over a small circleintermediate the ends of said cones propagating radially both inward andoutward to build an approximately spherical bulb having tangentialcontact with its cone and with the pavement.
 7. Equipment according toclaim 6 in which an open-mesh screen lies in each flame, said screenbeing of material adapted to emit radiation of relatively shortwavelengths efficient in heating light colored material.
 8. Equipmentfor heating the upper strata of asphalt concrete pavement, or the like,comprising chamber-forming walls including a roof wall adapted tooverlie an area to be heated by combined radiation and direct contactheating, and said walls including downwardly extending peripheral sidewalL portions that leave only a small crack between their lower edgesand said pavement; power air blower supply and heating means forproducing a multiplicity of flames in said chamber below said roof;exhaust means having an exit flow path through said chamber-formingwalls for removal of the products of combustion from within saidchamber, a mixing chamber to receive compressed air from said powerblower; fuel supply conduit means for delivering fuel to said mixingchamber; and a multiplicity of mixture conduits, one for each flame,receiving combustible mixture from said mixing chamber and delivering toeach flame its aliquot portion of mixture.
 9. Equipment according toclaim 8 in which said fuel supply conduit means has a portion havingheat transfer contact with said blowtorch for preheating the fuel enroute to said mixing chamber.
 10. Equipment for heating the upper strataof asphalt concrete pavement, or the like, comprising chamber-formingwalls including a roof wall adapted to overlie an area to be heated bycombined radiation and direct contact heating, and said walls includingdownwardly extending peripheral side wall portions that leave only asmall crack between their lower edges and said pavement; power airblower supply and heating means for producing a multiplicity of flamesin said chamber below said roof; exhaust means having an exit flow paththrough said chamber-forming walls for removal of the products ofcombustion from within said chamber, and conduit seeding means providedfor returning to the inlet of said power blower a minor fraction of thefresh exhaust gases from said chamber.
 11. Equipment for heating theupper strata of asphalt concrete pavement or the like comprisingchamber-forming means including a roof for overlying an area to receivethe heat and downwardly extending wall portions that leave only a smallcrack between said wall portions and said area, means for producing amultiplicity of closely spaced flames substantially in said chamber suchthat the flames substantially entirely fill the chamber with lambentflame, and means defining an exit flow path through said chamber-formingmeans for the removal of the products of combustion within the chamber;the wall surface of said chamber being of a material that radiates amajor portion of its radiant heat at red and infra-red wavelengths, andsaid chamber also containing a multiplicity of members associated withrespective flame producing means for radiating a substantial amount ofenergy in the visible spectrum above red.